chaining of several constructors c#

Question

I did some Google search but could not find anything. So I implemented something working with an intermediate constructor.

However, I am wondering whether it is possible to chain more than one constructor at the same time (base + this).

This is my current (simplified) code:

public BlaNode(Node Previous, Node Next) : base(Previous, Previous)
{
    this.Blas = new HashSet<BlaDiBla>();
}
public BlaNode()
    : this(null, null)
{

}
public BlaNode(Node Previous, Node Next, string Bla)
    : this(Previous, Previous)
{

}

Is this not working for you already?

Mike Perrenoud
– Mike Perrenoud

2012-08-02 13:09:38 +00:00
Commented Aug 2, 2012 at 13:09 — Mike Perrenoud
– Mike Perrenoud, Commented Aug 2, 2012 at 13:09
yes it is but I may not need the intermediate constructor.

cs0815
– cs0815

2012-08-02 13:10:46 +00:00
Commented Aug 2, 2012 at 13:10 — cs0815
– cs0815, Commented Aug 2, 2012 at 13:10

O. R. Mapper · Accepted Answer · 2012-08-02 13:13:41Z

1

No, you can only call one constructor at a time in a C# constructor initializer. The documentation refers to only one other constructor to call, too:

All instance constructors (...) include an invocation of another instance constructor (...). The constructor to implicitly invoke is determined by the constructor-initializer:

You can make your intermediate constructor private if you do not want any other code to call it.

answered Aug 2, 2012 at 13:13

O. R. Mapper

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Comments

Henk Holterman · Accepted Answer · 2012-08-02 13:14:16Z

1

Whether it is possible to chain more than one constructor at the same time (base + this)

No. You can chain either sideways (this), and do so multiple times, or 'up' (base), exactly once.

Note that the notation is closely linked to the order in which the constructor-bodies will be executed.

Your BlaNode(Node, Node) is the one that 'picks' the base constructor. Suppose that BlaNode() was allowed to select a different base constructor. That would only lead to confusion about which ctor(s) will be used, and with what parameters.

So there would be no gain that I can see, and there definitely would be drawbacks.

edited Aug 2, 2012 at 13:14

answered Aug 2, 2012 at 13:12

Henk Holterman

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6 Comments

O. R. Mapper Over a year ago

How can you chain sideways multiple times? I think that statement is incorrect as for every constructor, you can only indicate one chained constructor, be it sideways or upwards.

Henk Holterman Over a year ago

One time per ctor of course. But the chained ctor can chain again, as in the OPs question.

O. R. Mapper Over a year ago

So can the ctor chained upward.

Henk Holterman Over a year ago

But you can only execute one : base() per class. And multiple : this()

O. R. Mapper Over a year ago

Sorry, that's wrong. You can execute as many base() in the constructors of one single class as you like. Sometimes, that's even kind-of a pattern: When deriving from Exception, it's often the most reasonable way to declare four constructors with the four default signatures as found in the base class, and have each of them call the respective inherited constructor with the same signature.

|

Jan · Accepted Answer · 2012-08-02 13:26:19Z

1

As far as I know this is not possible. You can use static factory methods for this. http://en.wikipedia.org/wiki/Factory_method_pattern

private BlaNode(Node Previous, Node Next) : base(Previous, Previous)
{
    //whatever you do
}

public static BlaNode BlaNodeFactory()
{
    return new BlaNode(null, null);
}

public static BlaNode BlaNodeFactory(Node Previous, Node Next, string Bla)
{
    return new BlaNode(Previous, Previous);
}

edited Aug 2, 2012 at 13:26

answered Aug 2, 2012 at 13:15

Jan

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1 Comment

O. R. Mapper Over a year ago

They are not quite equivalent, though, as they cannot assign values to readonly fields.

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